Left winger Alex is confident of recovering from an ankle problem in time to play in Japan's World Cup opener against Australia on June 12.
The Brazilian-born star suffered the injury during Japan's drab 1-0 friendly victory against Malta on Sunday, but does not believe it is serious.
"I might have sprained my left ankle lightly," said the 28-year-old.
"I've got the foot iced up at the moment but I should be okay for the Australia game and will see what the situation is tomorrow."
Japan coach Zico is desperate for Alex to make a swift recovery as right winger Akira Kaji is likely to miss the clash with the Socceroos.
Kaji injured an ankle when he was on the wrong end of a tough tackle from Bastian Schweinsteiger during last week's 2-2 draw against Germany.
He has made some progress in his recovery, but admitted: " I am not sure about the opening match."
Zico left first-choice strikers Naohiro Takahara and Atsushi Yanagisawa out of the side to face Malta because of worries about their fitness but expects both to line-up against Australia.